Development of Fiber-Optic Fabry-Perot Interferometric Acoustic Sensor With Cavity Length Modulation

Diaphragm-based fiber-optic acoustic sensor achieves high sensitivity by detecting the vibrational displacement of the diaphragm center caused by incident sound. However, their sensitivity can easily be reduced by changes in ambient temperature, especially for fiber-optic Fabry-Perot (FP) interference microphones, as changes in temperature cause their operating point to deviate from the quadrature point (Q-point) of the interferometer. In this paper, by using a piezoelectric transducer (PZT) to monitor and modulate the temperature drift of the cavity length, a Q-point stabilized fiber-optic FP interferometric microphone is developed. The Q-point stabilization is achieved by feedback suppression of the second harmonic component I_2f(where f is the operating frequency of PZT) in the microphone frequency response curve. Experimental results show that the ratio of I_2f to I_f can be controlled below 5% in a wide temperature range of -10 ℃ and 50 ℃, and the resulting microphone exhibits high sensitivity and high fidelity to the incident sound signal.